Installation of inflatable occupant restraint systems, generally known as xe2x80x9cairbagsxe2x80x9d, as standard equipment in all new vehicles, has intensified the search for smaller, lighter, less expensive restraint systems. Accordingly, since the inflator used in such systems is the heaviest and most expensive component of an inflatable occupant restraint system, there is a need for a lighter and less expensive inflator.
A typical inflator comprises a cylindrical steel or aluminum housing having a diameter and length related to the vehicle application and characteristics of the propellant contained therein. The inflator is generally provided with an internal filter comprising one or more layers of steel screen of varying mesh and wire diameter. Gas produced upon combustion of the propellant passes through the filter before exiting the inflator. Co-owned U.S. Pat. Nos. 5,628,528 and 5,622,380, herein incorporated by reference, exemplify inflators having internal filters.
However, known internal filters are, of necessity, relatively heavy due to their disposition in close proximity to the propellant. The high gas temperatures produced upon combustion of the propellant dictate the use of relatively heavy wire mesh to preclude burn through. In addition, since it is desirable to maximize the pressure and volume of the gas entering the airbag in relation to the size of the inflator, pressure attenuation upon passage of combustion gases through the filter must be minimized.
The solution to the problem of reducing airbag inflator size, weight, cost and efficiency, in accordance with the present invention, is predicated on the concept that it is possible to utilize a relatively small and lightweight filter if it is disposed externally of the inflator housing and properly orientated relative to the gas discharge apertures in the inflator housing. Moreover, external orientation of the filter in spaced relation to the gas discharge orifice of the inflator effects expansion and cooling of combustion gases, minimizes heating of the filter and minimizes pressure drop in the gases emanating from the inflator.